Variable ratio die cast pulse transformer



Dec. 23, 1969 W A, KLEIN 3,486,149

VARIABLE RATIO DIE CAST PULSE TRANSFORMER f 41o BY ATTORNEY Dec. 23, 1969 W. A. KLEIN VARIABLE RATIO DIE CAST PULSE TRANSFORMER Filed Jan. 15, 1968 5 Sheets-Sheet z Dec. 23, 1969 W. A. KLEIN 3,486,149

VARIABLE RATIO DIE CAST PULSE TRANSFORMER Filed Jan. 15, 1968 's sneetsfsheet :s

United States Patent O 3,486,149 VARIABLE RATIO DIE CAST PULSE TRANSFORMER William A. Klein, Wappingers Falls, N.Y., assignor to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Jan. 15, 1968, Ser. No. 697,956 Int. Cl. H01f 15/10 U.S. Cl. 336-192 25 Claims ABSTRACT OF THE DISCLOSURE The technique of the present invention represents an improvement on the technique disclosed in copending application Ser. No. 698,031, led Ian. 15, 1968. The basic steps of the latter technique are followed in that the magnetic core is first encapsulated in a plastic molding and then the conductors for defining the windings are die cast into grooves or channels that exist in the plastic encapsulant. The present invention improves upon the technique of the copending application by providing an arrangement which permits varying at will the number of turns for the winding or windings that are to be formed. This is accomplished by so molding the plastic encapsulant surrounding the core that several metal fiow paths are molded at the same time. One of these paths is selected to remain open so that in the die casting step metal will flow in this open path. As a result, interconnection is made selectively from a terminal pin to the windings so as to include a desired number of turns therein.

Background, objects and summary of the invention This invention relates to an improvement in the manufacture of ferro-magnetic devices, and more particularly, to the fabrication of annular bodies or cores having suitably disposed windings and adapted for use in pulse transformers, memory elements, and the like.

The present invention is more particularly concerned with the fabrication of inductors and transformers comprising toroidal cores, usually composed of ferrite material, surrounded by windings. The invention is also concerned with a techniqueY for so fabricating these devices that they are immediately ready for application, in the form of pulse transformers and the like, in electrical circuits.

The technique of the present invention is related to the technique disclosed in copending application Ser. No. 698,031, filed Ian. 15, 1968. In that copending application there is disclosed a technique which includes encapsulating the ferrite cores and forming not only their essential windings but also the connections therefrom to appropriate terminals. The technique therein disclosed is extremely advantageous in that it reduces the handling required in the manufacture of pulse transformers and the like and avoids the need of forming grooves in the ferrite material lof which the core is usually composed. Furthermore, it permits compensation of the dimensional variations between cores. In other words, it allows for quite wide variations in the sizes of cores. Even more irnportantly, it enables simplication of the die structures for fabricating the windings inasmuch as the plastic encapsulant serves to define the die recesses for receiving the metal conductors.

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In essence, then, the previously developed technique exploits the use of die casting for forming the windings on magnetic cores and so reduces the handling required that great ease and speed in the manufacture of the cores is achieved with consequent great economies in the manufacture. However, it is highly desirable in the manufacture of pulse transformers and the like that the total number of turns on the transformer can be changed at will so that a great variety of transformers may be turned out with the same basic equipment. Thus, although it has been known to change the winding pattern by changing the mold that froms the plastic encapsulant surrounding the core, it has not been previously known to achieve a great variety of transformers, differing in turns and turns ratio, in a simple manner.

Accordingly, it is a primary object of the present invention to facilitate the varying of the number of turns for the winding or windings on a magnetic core device such as a pulse transformer.

Another object is to enable the selection of the number of turns in an extremely simple way, that is, to provide a method of making pulse transformers which permits establishing a great number of electrical winding configurations by using one mold.

The above-stated objects are fulfilled in accordance with the present invention by the provision of a specially molded plastic housing and by the technique of molding this plastic housing. The housing is so constructed that various combinations of flow paths can be selected for the fiow of the metal in the die casting operation. This die casting operation is, as alluded to above, performed at a later stage in order to form the windings for the magnetic core device.

It is a more specific feautre of the present invention that a technique is comprehended whereby the mold for forming the plastic encapsulant is designed to include a number of precisely located short or long pins. These pins are used in attaining the objective of having either a continuous or a discontinuous groove in the molded plastic encapsulant so that an open or closed flow path is created for the metal which is subsequently to be die cast. A long pin extends sufiiciently far so that the plastic material is ,prevented from owing and consequently a continuous groove is provided at that particular location. On the other hand, the short pins which are used do not extend sufiiciently to prevent the plastic material from fiowing in other grooves. As a result, the plastic flows in and causes these other grooves to be discontinuous. Thereby closed paths are created and the metal is prevented from flowing in the die casting step.

It will be appreciated, therefore, that the location of a long pin in the mold acts to select the particular groove to be filled with metal and hence determines the number of turns for a given winding. The detailed application of the use of these pins in fabricating pulse transformers and the like will be further appreciated as the description proceeds. However, it should be especially noted that this principle is specifically applied by having a plurality of selectively connectable grooves on one face of the plastic housing and spaced from a common groove, also on the same face, whose one end is connected to a terminal pin.

Briefly stated, the above-described technique of the present invention produces an electrical component such as a pulse transformer or the like which comprises an annular magnetic core surrounded by a molded plastic housing, the housing having a plurality of channels serially interconnected so as to define at least one helical winding path around the core. Metal conductors in the channels form the helical winding by virtue of the die cast ing operation. The component, in accordance with the present invention, includes means which form part of the plastic housing for selectively establishing a continuous groove for delining a flow path which will serve to interconnect a particular turn on a given winding With a terminal pin.

It should be noted that the present invention will be discussed hereinafter with reference to the embodiments in a special form of pulse transformer, namely, what is termed a discrete card pluggable transformer. By this is simply meant a unit which is so fabricated that it may be plugged into a circuit board or module or the like. However, it will be apparent that the concepts of the presentinvention are not necessarily limited to this particular form of device.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

Brief description of the drawings FIG. 1 is a perspective view, from the top face, of an encapsulated magnetic core device, in the form of a pulse transformer, prior to the die casting of the windings and interconnecting leads.

FIG. 2 is a cross-sectional view taken on the line 2-2 in FIG. 1 through the magnetic core device and through the plastic mold in which the magnetic core has been inserted.

FIG. 3 is a cross-sectional view of the die casting apparatus for die casting the windings and interconnecting leads onto the unit shown in FIG. l.

FIG. 4- is a top plan view of a completed pulse transformer, showing the die cast windings and interconnecting leads thereon.

transformer previously depicted in FIG. 4.

Description of preferred embodiments Referring now for the moment to FIG. l, an encapsulated core unit is illustrated. This is a molded unit which will eventually be provided with the necessary windings and interconnections, by means of die casting, to form a finished pulse transformer. The unit 10 comprises an annular magnetic core 12 which is completely surrounded by a plastic housing 14. The plastic housing 14 has an opening 14x defining its inner periphery and also is provided with extended portions 14y for purposes of providing standoff from a circuit board or the like when the finished component is to be plugged into a circuit.

A plurality of serially connected channels extend around the annular core 12 so as to deline at least one helical winding path. Since in the case illustrated here the molded unit 10 is destined to become a pulse transformer, which includes a primary and secondary winding, there are actually two helical winding paths formed around the core 12, as will be explained in detail hereinafter. Adjacent the outer periphery of the core 12 the channels just referred to comprise a series of perforations 16 which extend transversely through the plastic housing 14. Of course, with respect to the core 12 these are axially-extending. A series of axially-extending grooves 14 is formed at the inner periphery of the plastic housing and these extend in depth so as to approach the inner periphery of the core 12.

The helical lwinding paths which are to be filled in with metal in the die casting. operation are thus delined by the series of perforations 16, by the grooves 14 and further by the zig-zag pattern of grooves 20x and 20)/ which are formed on the top and bottom faces respectively of the housing 14. This can best be understood by reference to FIG. 4 Where the entire winding pattern can be comprehended. It will there be seen that the grooves 20x and 20y are oppositely skewed on the respective faces so as to define the required serial interconnection with the axially-extending perforations 16 and grooves 18. The separate helical winding paths have been designated with the circled A and circled B symbols for convenience in tracing out these paths. It will be noted that the pulse transformer can have as many as eleven turns for each of its windings, that is, eleven turns in the primary or A winding and eleven turns in the secondary. As the pattern shows, this is a bililar configuration for the windings.

On the top face of the molded unit 10l seen in FIG. l there is a series of spaced grooves 22a and 22b which extend generally longitudinally of the housing 14. These grooves are selectively connectable respectively to the laterally-extending grooves 24a and 24b adjacent opposite ends of the housing. This series of grooves, which connect with selected ones of the perforations 16, constitute a means for selectively establishing an open flow path for the metal which is to be die cast. In other words, they constitute a means forming part of the molded housing 14 for selectively connecting to one end of a winding so as to vary the number of turns in that winding on the pulse transformer to be fabricated.

On the bottom face of the housing 14, as best seen in FIG. 8, further grooves 30a and 30b extend inwardly to connect with grooves 18. The grooves 30a and 30b serve the purpose of connecting the oppo-site end of a given winding to a terminal for completing the required circuit path.

It can now be understood how the windings for the eventual pulse transformer are to be produced. rThus, a primary winding will extend completely around the magnetic core 12 and likewise a secondary winding. By reason of the provisions of the grooves 22a, 24a and the corresponding grooves 22b and 24b on the top face, as well as the grooves 30a and 30b on the lower face, the primary and secondary winding can be completed and brought out to connect with the pairs of terminal pins 26a and 26b. These pairs of pins are locked into place within the plastic housing 14. That is to say, they are molded in the housing at the molding stage depicted in FIG. 2. Contact with the embedded pins made by reason of the fact that pairs of respective apertures 28a and 28b are provided in the housing 14 and, as can be seen in FIG. 6, these extend transversely through the housing for the purpose just mentioned.

The required interconnections between the pairs of terminal pins 26a and 26b and their respective windings would normally be established by way of simple interconnecting leads. Here, however, as already noted, the interconnecting leads are in the form of metal conductors which will be die cast, for the primary winding, in the series of grooves 22a and in their common associated groove 24a; for the secondary, of course, the conductors will be disposed in the corresponding seriesof grooves 22b and the common groove 24b. Actual contact to the embedded terminal pins is by way of metal conductors in the apertures 28a and 28b.

Referring now to FIG. 2, there is illustrated a fairly conventional plastic molding apparatus 50 which is used for the purpose of producing the molded article of FIG. 1, that is, the encapsulated core unit 10 shown therein. The elements of this molding apparatus, outside of the mold itself, are well known in the art. These elements are seen to include a piston 52 for forcing plastic material 54 into a mold comprising the parts 56a and 56b. Also shown is a conventional upper platen 58. A chamber 60 in this upper platen communicates with passageways 62 in the upper part 56a of the mold. This allows iiow of the plastic material 54 into the mold cavity 64 as the piston is driven down.

Before the parts 56a and 56b are brought together for the actual molding operation, the annular core 12 is inserted in the lower part 56b. This part is specially shaped at its central portion 561. Also, specially formed pins or chairs, not seen, are provided for the purpose of properly positioning and supporting the core within the mold cavity. The result of the presence of the supporting pins or chairs is that recesses 29 are formed in the housing 14.

The interior of the mold is specially shaped for proper molding of the core unit that is to be produced. The surfaces of the cavity 64 provided in the die are complementarily formed with respect to the desired conliguration, as already described, of the unit of FIG. 1. Thus, the side walls, bottom and top of the cavity are provided with the necessary series of projections or ridges 66 which serve to define the various grooves for forming the windings; that is, the helical-path-deiining grooves 18, x and 20), and also the grooves 22a, 24a, 22b and 24b for defining the interconnecting leads from the windings to the terminals. A series of pins 68 serve to define the perforations 16 which, as noted before, are for the purpose of producing the axially-extending outer peripheral metal conductors for the windings. The portions 56x and 56y of the mold, which meet when the molded parts 56a and 5617 are brought together, are provided in order to denne the apertures 28a and 28b which serve for the purpose already indicated.

The unique configuration which results for the molded plastic housing 14 may be appreciated by reference to the short and long pins 70 and 72, as seen in FIG. 2. A plurality of each of these pins is provided and these are distributed selectively in the upper part 56a of the mold so that the grooves 22a and 22b can selectively be made either continuous or discontinuous depending upon the particular number of turns that are desired for the pulse transformer being fabricated. A long pin 72, held at one end in a suitable receiving bore, extends suiiiciently far so as to project through a suitable aperture in a ridge 66 which defines a predetermined groove 22a. This long pin extends such that plastic material is prevented from iiowing so as to create a continuous groove in the housing. In other words, because of the length of this pin 72 a continuous groove 22a including the cylindrical recess 23a, is provided. Therefore, by this arrangement, that is, by having the long pin at a certain location a continuous ow path results at that location for the metal to be subsequently die cast.

For purposes of illustration, the particular configuration in FIG. 1 provides full turns on each of the primary and secondary windings. That is, the lowermost grooves of each of the series of grooves 22a and 22h has been made continuous by reason of the fact that the long pins 72 are located in the corresponding apertures in the ridges 66 which define these lowermost grooves. At all of the other locations the short pins 70 have been employed with the result that all the other grooves 22a and 2211 are discontinuous because of the presence of the plastic material which is permitted to flow.

It will be apparent that simply by changing the locations of these long pins 72 any one of a number of metal flow paths can be established. Thus, if it is desired that the primary winding have only a single turn the long pin would be disposed at a location such that the next adjacent groove 22a would be rendered discontinuous.

It will be understood that when the mold parts 56a and 56b have been brought together and the plastic material 54 is forced into the mold, all of the spaces remaining between the core 12, as it is positioned within the mold cavity, and the surfaces of the cavity will be completely filled with the plastic. Consequently, the core 12 is completely surrounded by the plastic encapsulant to produce the unit of FIG. 1 and the pins 26a and 26b become embedded Within the plastic housing 14. This embedding of the pins can best be seen in FIGS. 6 and 7.

A thermosetting plastic has been found to be the most useful type of material in fabricating the plastic housing 14; in particular, an epoxy resin is not suitable for encapsulating the core 12 in this manner. Epoxy resin, of course, is an insulator and thus the required function of insulating the conductive ferrite core 12 from its windings is also served by the use of this material. The temperature that is selected for use in the plastic molding apparatus is of the order of 340 F., and preferably is selected to be between 290-360" F.

It should be noted here that the drawings exemplify a single-cavity mold for the purpose of producing the unit 10 but this has been done merely for the sake of simplicity in explaining the principles of the invention. It will be understood that multiple-cavity molds would be utilized for high production operations. It will also be appreciated that the molding operation just described, for producing the encapsulation of the core 12 affords a very significant advantage in compensating for variations in the dimensions of cores where great numbers of these are involved. Accordingly, it is not necessary that all of the magnetic cores that are to be encapsulated as described be first rigidly inspected and then be brought to within very precise tolerances. Rather, the cores can be brought within wide dimensional limits, and thereafter supplied to the molding apparatus. As the cores emerge from the molding apparatus they will perforce be closed to being identical since they are all being molded in the same or similar mold.

Because of the complementarily-formed molding surfaces within the m-old, the various grooves, perforations and the like are now completely ready for the reception of metal to define the iinal product. As noted before, the channels that have been created to surround and extend entirely around the annular core are serially connected so as to form the desired continuous helical path. Thus, taking a typical groove 18, which extends axially of the core 12 at the inner periphery thereof, one end of this groove connects with a skewed groove 20x at the top surface of the plastic case 14. The other end of this groove 20x connects with a perforation 16 whose other end, in turn, connects with a skewed groove 20y which is oppositely skewed on the lower face of the plastic housing 14. It will be seen that the next serially connected groove 18 is spaced two grooves away from the groove 18 initially considered. Thus, the primary winding works its way around the core in alternating fashion with the secondary winding to produce the already-noted bitilar configuration.

After removal of the molding flash from the unit 10 the next step is the die casting operation. The molding ash inevitably results and is handled in a conventional manner. Referring now to FIG. 3 the die casting operation is herein illustrated. The die casting apparatus for this purpose is fairly conventional. However, it should be pointed out that the unit being handled is extremely small having dimensions in the order of 1/2 by 1A by 1/s". Also it will be apparent to one skilled in the art that the die casting about to be performed results in a completely finished magnetic component that will then be immediately available for placing into service. In other words, everything has been done that is required in order to form a finished component and now all that remains is a one-shot operation, so to speak, to fill in all of the grooves, apertures and perforations that have been provided in the molded plastic housing 14. Another way of saying this is that a unitary or integral die casting operation is about to be performed so that the windings, interconnecting leads, etc. will be completely formed on the unit 10.

The encapsulated core unit 10 is sandwiched between two heated die casting die sections 400a and 400b and a clamping force of approximately 1,000 pounds is applied. The die is usually heated to the temperature of approximately 440 F., depending on the metal used. It has been found that with temperatures that are lower than this, problems result from the fact that metals tend to solidify atv the entrance to the die or the fiash produced is too great or the metal moves too rapidly or the die does not fill properly. The best metal composition that was found for the present purposes is a tin-silver alloy and the percentage of silver was varied from about upward to about Here, again, although for the sake of simplicity only one core unit has been considered, the technique is perfectly amenable to high production operations and thus a great number of these core units 10 would be processed simultaneously.

The metal in the form of the aforesaid silver-tin composition is injected into the die by means of the conventional conduits 410, and then pressure is brought to bear so as to result in forcing the silver-tin composition into all the already-defined grooves, perforations and apertures. The die casting herein entailed has the inherent advantage of extreme simplicity of construction for the die 400 inasmuch as the metal is being forced into grooves, perforations, etc. already formed in the plastic housing 14 rather than into specially-formed slots or grooves in a steel die. Thus only a smoothed-surfaced cavity is required within the die 400.

Referring to FIGS. 4 through 8, there is illustrated the finished conponent of the present invention, that is, a pulse transformer having its windings, interconnecting leads and all else that is required completely formed. The component is therefore ready for placing into immediate service. As a result of the die casting operation, first of all, the conductors 118 have been disposed in their grooves 18 provided for this purpose. Also, the conductors 116 in the perforations 16, and the skewed conductors 120x and 120y in their respective grooves. Thus the two windings, that is, the primary and secondary winding are completely defined and extend completely around the core 12.

The interconnecting leads at the top face of the housing 14 result from the disposition of the metal conductors 122a and 122b and the metal conductors 124a and 124k in their respective grooves. The conductors at the bottom face of the housing 14, that is, conductors 130a and 130b are in their grooves 30a and 301;, respectively.

Because of the particular selection and location of the long pins 72, that is, because of their location in the mold, as described, the conductor portions 123a and 123b are `formed in the respective cylindrical recesses 23a and 23h and, hence, there are continuous metal paths which can be appreciated by reference to FIG. 4. lt will also be seen there that metal conductors 128a and 128b are disposed in their respective apertures 28a and 28h. It will be manifest that two electrically-complete windings with their full number of turns have been produced.

Because of the space limitations in providing the grooves 22a, 22b and their associated common grooves 24a, 24b on the top face of the plastic housing 14, only a limited number of possible combinations of turns can be realized for the primary and secondary windings. However, if it is desired that the whole gamut of selectability of turns be provided, a convenient way to `do this would be to provide a complementary configuration of similar grooves on the opposite or bottom face of the housing 14. This complementary configuration would serve to connect the terminals to other points corresponding to the other turns on the primary and secondary windings. Thereby, any number of turns from either winding could be selected.

In the event that it may be found desirable to improve the response time for a pulse transformer provided by the basic teachings of the present invention, a modification may be followed. This modification or alternative embodiment would reduce the inductance involved by interrupting a given winding at a point subsequent to the point at which the continuous groove 22a or 22h makes contact to a perforation 16. This can be simply achieved as follows: since the perforations 16 are defined in the mold by the removable pins 68, it is a simple matter to remove one of these pins at the desired point, thereby breaking the winding. In other words, with the pin removed from the mold at this location, the perforation normally provided will be filled in with plastic material and, hence, the winding will be rendered discontinuou at this juncture.

What has been disclosed herein is a novel technique which allows for making a great variety of electrical configurations for a magnetic component from a single plastic mold. This magnetic component is preferably in the form of a pulse transformer, comprising a ferrite core or the like encapsulated in a plastic housing. Appropriate grooves, perforations, and the like are molded into the housing which becomes part of the die for the die casting of metal to define the windings, interconnecting leads, etc, Because of the formation of specially-selected grooves, various combinations of flow paths for the die cast metal can be selected and, thus, the total number of turns on the transformer can be very easily changed. Moreover, the turns ratio can be changed; also, the primary inductance, the winding resistance and interwinding capacitance, As a consequence, an extremely versatile pulse transformer can ybe produced by the technique of the present invention.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is: 1. A process of fabricating a variable turn magnetic core device comprising the steps of providing an annular magnetic core; molding a plastic encapsulant to surround the annular core, said encapsulant being provided with a series of interconnected channels defining at least one helical winding path around said core; and concurrently molding a plurality of grooves, selective ones of which are discontinuous, for providing a selective flow path for interconnecting metal conductors forcing metal into all of the channels and grooves thus formed in the plastic encapsulant, thereby to form at least one winding and at least one interconnecting lead.

2. A process as defined in claim 1 in which a plurality of terminal pins are molded in said plastic housing.

3. A process as defined in claim 1 in which the metal is die cast into the already formed channels and grooves.

4. A process as defined in claim wherein said metal is a silver-tin alloy.

5. A process as `defined in claim 4, wherein said alloy comprises 5-15% silver.

t6. A process as defined in claim 4, wherein the temperature for molding the plastic encapsulant is of the order of 340 F. and the temperature for die casting is of the order of 440 F.

7. A process of fabricating a magnetic core device as defined in claim 1 further comprising the steps of inserting an annular magnetic core into a plastic mold,

said mold being provided with a plurality of pins, some of which extend sufficiently far to prevent the iiow of plastic material such that a continuous groove is provided in one face of the plastic housing and a plurality of discontinuous grooves are also provided and forcing metal into the plurality of grooves thus formed in the plastic housing whereby the metal fiows only in the continuous groove so as to complete a conductive path.

8. A process of fabricating a variable turn magnetic substrate device comprising the steps of providing a lmagnetic substrate;

molding a plastic encapsulant to surround the magnetic substrate, said encapsulant being provided with a series of interconnected channels defining at least one helical winding path around said substrate; and concurrently molding a plurality of grooves, selected ones of which are discontinuous, for providing a selective iiow path for interconnecting metal conductors;

forcing metal into all of the channels and grooves thus formed in the plastic encapsulant, thereby to form at least one winding and at least one interconnecting lead.

9. An electrical component comprising:

an annular magnetic core surrounded by a continuous unitary I molded plastic housing;

a series of channels in said plastic housing interconnected so as to define at least one ow path for metal to establish a helical winding around said annular core;

metal conductors in said channels spaced from said core by said housing, forming said helical winding for said core; and

means forming part of said housing for selectively establishing a continuous groove therein for varying the number of turns in said winding.

10. An electrical component as defined in claim 9, wherein said channels are in the form of perforations adjacent the outer periphery of said core and in the form of axially extending grooves adjacent the inner periphery thereof, and in the form of skewed grooves, on the upper and lower plane faces of said housing.

11. An electrical component as defined in claim 10, wherein said magnetic core is of ferrite.

12. An electrical component as defined in claim 11, wherein said plastic housing is constituted of a thermosetting plastic.

13. An electrical component as defined in claim 12, wherein said thermosetting plastic is an epoxy resin.

14. An electrical component as defined in claim 9, wherein said means forming part of said housing comprises ,a plurality of grooves defining selectively continuous flow paths for metal conductors, each groove defining a separate path connected to a selected point on said winding.

15. An electrical component as defined in claim 9, wherein said metal conductors are formed of a silver-tin alloy.

16. An electrical component as defined in claim 9, further including a plurality of terminals extending from said plastic housing; interconnecting leads from said terminals to said winding.

17. An electrical component as defined in claim 16, wherein at least one of said interconnecting leads comprises a plurality of conductors extending from individual turns on said winding; a common conductor connected to one of said terminals, said common conductor being connectable to selected ones of said plurality of conductors.

18. A pulse transformer comprising an annular magnetic core surrounded by a continuous unitary molded plastic housing; a plurality of channels in said plastic housing serially connected to define a plurality of helical winding paths around said core; metal conductors in said channels, spaced from said core by said housing, forming at least a primary and a secondary -winding for said transformer; and means for forming part of said housing for selectively establishing a continuous groove therein for varying the number of turns selectively in said primary and secondary windings.

19. A pulse transformer as defined in claim 18, wherein said channels are in the form of perforations adjacent the outer periphery of said core, in the form of axiallyextending grooves adjacent the inner periphery of said core, and in the form of skewed grooves on the upper and lower faces of said housing.

20. A pulse transformer as defined in claim 18, wherein said means forming part of said housing comprises a plurality of grooves defining selectively continuous flow paths for metal conductors, each groove defining a separate path connected to a selected point on said winding.

21. A pulse transformer as defined in claim 18, wherein said metal conductors are formed of a silver-tin alloy.

22. A pulse transformer as defined in claim 21, further including a plurality of terminals extending from said plastic housing; interconnecting leads from said terminals to said winding.

23. A pulse transformer as defined in claim 22, wherein at least one of said interconnecting leads comprises a plurality of conductors extending from individual turns on said winding; a common conductor connected to one of said terminals, said common conductor being connectable to selected ones of said plurality of conductors.

24. An electrical component comprising:

a magnetic substrate surrounded by a continuous unitary molded plastic housing;

a series of channels in said plastic housing interconnected so as to define at least one helical iiow path for metal to establish a winding around said substrate;

metal conductors in said channels, spaced from said substrate by said housing, forming said helical winding for said substrate; and

means forming part of said housing for selectively establishing a continuous groove therein for varying the number of turns in said winding.

25. A pulse transformer comprising:

a magnetic substrate surrounded by a continuous unitary molded plastic housing;

a series of channels in said plastic housing interconnected to define a plurality of ow paths for metal to establish a plurality of windings around said substrate;

metal conductors in said channels, spaced from said core by said housing, forming at least a primary and a secondary winding for said transformer; and

means forming part of said housing for selectively establishing a continuous groove therein for varying the number of turns selectively in either of said primary and secondary windings.

References Cited UNITED STATES PATENTS 1,603,416 10/1926 Schackelton 336-229 XR 2,818,514 12/1957 Goertz et al. 336-96 XR 3,155,766 11/1964 Eichert et al 336-96 XR 3,251,015 5/1966 Denham 336-96 3,319,207 5/1967 Davis 336-229 LEWIS H. MYERS, Primary Examiner T. I. KOZMA, Assistant Examiner U.S. Cl. X.R. 

